An HUD device to display a virtual image of a display light image representing vehicle-related information related to a vehicle by projecting the display light image with a projector and reflecting the display light image with a reflecting mirror has heretofore been known widely. By using a reflecting mirror in this way, a space occupied by an HUD device in a vehicle can be reduced substantially.
As such an HUD device, a device that adjusts a position of displaying a virtual image of a display light image by decelerating the rotation of a stepping motor with a reduction gear mechanism, transferring the rotation to a reflecting mirror, and thus driving the reflecting mirror is disclosed in Patent Document 1. In the device disclosed in Patent Document 1, a rotational position of a stepping motor is controlled in accordance with an adjustment instruction from an occupant of a vehicle and resultantly a position of displaying a virtual image of a display light image can be adjusted appropriately to a position expected by the occupant. In addition, in the device disclosed in Patent Document 1, in a reduction gear mechanism, a resilient member generates a restoring force in the direction of engaging transmission gears with each other and resultantly a backlash between the transmission gears disappears. As a result, a deviation caused by a backlash between transmission gears is not easily generated at a position of displaying a virtual image of a display light image.